I am the guy that told Redline not to use red oil. Here are some answers to your questions.
1. Speed is dictated by gpm at the work port of the cylinder and the bore of the cylinder. A bigger bore takes longer to fill, and thus is slower than a comparable smaller bore cylinder. You can go to a bigger pump (more gpm), but you need more engine to turn it. The biggest 2 stage pump available right now is 28gpm. That will take a 20hp engine to turn. You would also need bigger hoses and probably valve body. Valve bodies are rated for max gpm.
2. Power in a cylinder is determined by cyl. bore and psi output of the pump. Pi R squared times psi gives you your force. While your pump may have an adjustable pressure relief,, don't mess with it. Or set the pressure higher and wait for something oily and explosive to happen.
3. Never use synthetic oil in a hydraulic application unless it was made specifically for hydraulic applications. This oil and any red oil significantly shorten the life of seals made from buna rubber or urethane because of its detergent content. Your system has buna rubber and urethane. Red oil is used because of the cold flow characteristics, not because it's a good hydraulic oil. The manufacturer doesn't want you blowing up the pump on a cold morning.
Dedicated hydraulic oil has anti-wear, anti-oxidation anti-foam additives. Red oil doesn't. Oils rated with the AW designation are fine to use in your system. AW 20 is light, AW 32 is a good all-around weight, and anything higher is strictly warm weather, 70 degrees or warmer.
I love red oil because it creates work for my shop. But brown oil is the way to go.
Your speed is what it is unless you're willing to spend $$ or ignore safety.
Bert